Process for plating a selective surface within a groove



Dec. 26, 1961 c. H. BOMMERSCHEIM 3,014,851

PROCESS FOR PLATING A SELECTIVE SURFACE WITHIN A GROOVE Filed June 5,1959 2 Sheets-Sheet 1 v INVENTOR. CAM/P15 HW/P) BO/VME/PSCHHM 1961 c. H.BOMMERSCHEIM 3,014,851

PROCESS FOR PLATING A SELECTIVE SURFACE WITHIN A GROOVE Filed June 5,1959 2 Sheets-Sheet 2 Ilirlliii w E5. v f fi IN V EN TOR "in! lidrlr z.iillvi hmu-lruun- ATTOf/VFY United States Patent 3,614,851 PROCESS FGRPLATING A SELEGHVE SURFAGE WITHIN A GRUQVE Charles Henry Bomrnerscheini,Kalamazoo, Mich, assignor to Savage Plating & Anodizing Co., lino,Kalamazoo, Mich a corporation of Michigan Filed June 5, 1959, Ser. No.818,287 6 Claims. (Cl. 264-) This invention relates to a process andapparatus for the metal plating of a selective surface within a groovewhich is normally subject to wear and/or corrosion.

Theprimary object of the invention is to provide an efiicient andpractical method of plating a selective surface of a dimensionally deepand/or narrow groove in such a manner that the plating is of controlledand uniform thickness across the entire selected surface withoutrequiring regrinding or resurfacing after plating.

It is well known that the horizontal land surfaces of cast iron dieselengine and other pistons are subject to wear and/or corrosion. Hence,these land surfaces should be plated with a corrosion and wear resistantmetal, such as hard chromium, in thicknesses to meet tolerances.

Heretofore, conventional methods of plating the lands of the ringgrooves of pistons have been unsuccessful. For example, when the pistonis held in a vertical position and made cathodic and a parallel verticalanode is positioned one to twelve inches therefrom, metal will notdeposit on the selected land surface of the ring groove withsufficiently uniform distribution as to coatihg thickness. Because thegroove is dimensionally deep and/or narrow, the deposited metal willbuild up preferentially at the edge of the surface closest to the anodewhile the portion at the bottom of the groove which is at the greatestdistance from the anode will receive little or no deposit.

If an attempt is madeto plate the surfaces within the grooves normallysubject to wear and/or corrosion by anodes positioned within the narrowring grooves, dif- I Patented Dec. 26,1961

FIGURE 1 is an elevational view of apparatus illustrating the presentmethod of plating'a selected surface of the ring groove of a piston;

FIGURE 2 is a sectional view taken on the line 2-2 of FIGURE 1;

FIGURE 3 is an enlarged vertical sectional view through a pistonillustrating the manner of affixing the insoluble anode to the piston inpositionto plate a se-. lected surface of the ring groove;

FIGURE 4 is a view similar to FIGURE 3 showing a modified form of theinvention; and

FIGURE Sis a fragmentary diagrammatic View of an alternative method ofapplying the anode to the piston.

Specific reference is now made to the drawings wherein similar referencecharacters are used for corresponding elements throughout. the inventionwill be described with reference to a cast iron diesel engine piston,the principles thereof are applicable to anymetallic grooved memberwhere it is necessary or desirable to plate one or more selectedsurfaces of the groove.

Indicated at 10 is a diesel engine piston Which, as is well known, is acylindrical cast iron'member having a plurality of axially spaced ringgrooves 12 which are relatively narrow and deep, the depth beingapproximately 0.25" and the average width approximately 0.253 to 0.255",the overall length of the piston approximating 9.781". When the pistonis operated in the engine, the rings in the grooves subject the landsurfaces 14 thereof to wear'and corrosion which, if not corrected,eventually causes cracking of the rings. Hence, itis desirable thatthese land surfaces of the new pistons be protected ficulties arise.Thus, if the anodes are lead foil or wire,

a short circuit will occur with arcing and injury to the surface anddeposit. Moreover, lead wire of sufficient size tocarry current wouldinhibit the entrance of fresh electrolyte and might lead to localizedoverheating of the electrolyte plus. depletion. These considerationsalso preclude the possibility of supporting and accurately positioning adelicate anode structural shape Within a narrow ring groove around thecircumference of a piston by means of an outside structure andmaintaining accurate spacing between the anode and the surface to beplated.

The present invention overcomes the aforementioned difficulties' byusing an insoluble anode whichis con formable to the contour of thegrooved member and which is fixed to but insulated from the groovedmember in such a mannerthat the anode covers the surfaces of the groovenot to be plated but opposes the selected surfaces to be plated, thegrooved member itself serving to-support the anode. By making thegrooved member a'cathode and immersing the same in a suitableelectrolyte. a uniform controlled thickness of such metals as chromium,nickel, copper, tin, zinc, silver, gold or cadmium can be deposited onthe selected surfaces of the grooves.

The principles of the invention will best be understood with referenceto the accompanying drawings, wherein:

against wear and corrosion by a metal plating, preferably hard.chromium. However, the deposited metal must be of controlled and uniformthickness coextensive with the land surface, generally in the order ofmagnitude of 1 to 2 mils and the present invention accurately andefficiently accomplishes this without the necessity of regrinding orresurfacing of the deposited metal.

A suitable vessel or tank lfi is provided in which is supported a steelrack 18, preferably U-shaped, the rack in turn supporting the piston 10in a vertical position, the rack including vertically extendinginsulating mem bers 20. The steel members 22 passing through theinsulation include horizontal portions which engage the lower end of thepiston 19. Mounted upon a flange or other support on the upper end ofthe tank are insulators 24 whch in turn mount two copper buses 26, theupper ends of the vertical portions of the steel rack members 22 hookingaround and contacting the copper buses, the latter being operativelyconnected to a current source (not shown) which is negative when platingtakes place thereby rendering the piston cathodic.

The insoluble anode employed in the process is such as to be-conformableto the configuration of the piston and readily affixable but insulatedfrom those portions'of the piston which are not to be plated so that theanode is automatically retained by the piston in a desired positionadjacent to but opposite the surface or surfaces to backedinsoluble leadtape is preferred, the same being also satisfactory for nickel platingfrom a chloride-free nickel-sulfate bath or copper plating from aconventional acid copper-sulfate bath. A low carbon steel or alloy steeladhesive backed tape may alsob'eiused for plating copper, tin, zinc,silver, gold or cadmium from convenl Patent Re. 23,843. f

lt'should 'be understood that while ofthe type disclosed in U.S,

In practice, the land surface 14 to be plated should be given asatisfactory surface finish. In the case of new pistons, the surfacefinish should be 32 micro inch R.M .S. or better. In the case of wornpistons, the surface finish ,should be 16 micro inch R.M.S. or betterbecause of the greater thickness of metal deposit which is normallyrequired. The piston is then vapor degreased and an insulating strip 28,such as pressure sensitive tape for electroplating which is disclosed inUS. Patent Re. 23,843, v

is applied around the piston to all of those surfaces which are not tobe plated, the lower free edge 30 of one strip portion thereofterminating immediately above the land surface 14 to be plated.

The adhesive backed lead tape 32 is then applied to the insulating strip23 in parallel strips with respect to the piston axis which overlap(shown exaggerated in FIGURE 3) starting approximately half way up thevertical surface 34 of the groove with the land 14 to be plated, as "at36, then across the horizontal surface 38 ofthe groove opposite the land14, then up the outside surface 40 of the piston where it terminates ator below the upper transverse surface 42 of the piston as at 44.lfnecessary, the overlapped strips of lead tape 32 are ultimatelysmoothed out. A lead wire 46 is then wrappedaround the, upper portion ofthe tape 32 gripping the outside of the piston firmly to make positiveelectrical contact. One or more lead wires 48, see FIGURES 1 and 2, arethen carried a sufficient distance above the piston for operativeconnection to an outside current: source whereby the. tape is renderedpositive, during the plating operation.

It is to be understood that the lead tape 32 may be applied to thepiston in a series of vertically extending, overlapping strips whoselongitudinal axes extend axially ot the piston as shown. in FIGUREinstead of in a series of horizontally extending strips whose axesextend circumferentially aroundthe piston as. shown in FIGURE 3. Theadhesive backing of the tape may be. conductive or insulating. If the.adhesive backing is conductive, the tape may be applied in overlappedhorizontal layers and have adequate, conductivity both vertically andhorizontally. If, the adhesive backing is. insulating, the tape may beapplied in overlapped vertical layers and. have adequate verticalconductivity.

In the modification shown in; FIGURE 4', the lead wires 46 may be,stopped off with. an insulating masking tape 50 which terminates at thecorner 52. representing the juncture of the. horizontal surface. 38 ofthe groove opposite the land 14. and the. vertical outer surface 40. otthe piston as a further means of confining current flow to the lead tapesurface within. the, ring groove itself. This more closely controls thedistribution of metal to be deposited upon, the bottom horizontal orland surface 14.

In the process of plating the land surface 14 with chromium, the. vapordegreasedpiston is supported, as

described hereinabove, in'a chromic acid plating bath 54. Before doing;so, the. land is preferably vapor blasted to produce an oxide-freesurface. The piston is, first electrically connected to the positiveterminal of a suitable D.C. source, such for exampleas 6 volts, the leadtape electrode 32 being connected to the, negative terminal by. means ofthe. lead wires 48. The land. surface 14 is then given a conventionalreverse" etch at about 0.5-3 a.s.i. (72 to 432,a.s.f.)' for one-half toseveral minutes. The electrical connections are then quickly reversed,preferably by a reversing switch, and the land surface 14 is chromium,platedsusing the exposed surface of the lead tape 32 as the. insolubleanode.

The composition: of the, chromium bath is not critical and currentdensities and temperatures of conventional valuesmay be employed. Thesame is true when the land surface is to be plated with nickel, copperand other metals as. mentioned hereinbefore. Satisfactory chromiumplating of the land surfaces of cast iron diesel engine i pistons wasaccomplished with a temperature of l 32" F. using a bath containing 36oz./gal. of chromic acid with sufficient sulfuric acid to give a ratioof CrO to H 80 of 100 to l. The current density must be varied in aconventional manner depending upon the temperature and the basis metal.Values of 0.5 to 3 a.s.i. (72 to 432 a.s.f.) may be used for copper,nickel and most steels. Lands of cast iron pistons were successfullyplated by first striking for 1.5 to 2 minutes at 9 a.s.i. (1296 a.s.f.)and then continued deposition at 3 a.s.i (432 a.s.i.).. Steel pistonswere successfully plated at the latter value without striking.

By the present invention, lands of new diesel pistons have been platedwith 0.5 to 1.0 mil chromium wherein the coating of the deposited metalwas sufiiciently uniform over the entire land surface 14 to meettolerances, thus eliminating the necessity of costly and difiicultregrinding after plating. These pistons showed no appreciable wear onthe plated lands after 1,000 hours test run.

It should be understood that the invention may also-be employed tosalvage worn pistons in which case the ring groove has been ground togive a true surface with a finish of 16 micro inch R;M.S. or better andchromium has been deposited up to a thickness of 6-12 mil which is notlimiting; These heavier coatings may require regrinding to meetdimensional requirements, but even if they do such regrinding will beminimal since, by the present process, the thick chromium depositissubstantially uniform across the entire face of the land surface.

While a preferred embodiment of the invention has here been shown anddescribed, skilled artisans may-make minor variations without departingfrom the spirit of the invention and the scope of the appended claims;Thus, it should be understood-that while it is the landsof pistons.which are normally subject to wear and/ or corrosion and thereforerequire plating, the invention is applicable to. any metallic groovedmember for the plating of any one or more surfaces of the groove whichrequire a protective coating of metal.

- I' claim:

1. A process of electroplating a selective surface.

afiixing via insulating adhesion an insoluble deformable.

. metallic Inemberto the surfaces of the groove which are.

not to be plated, said member conforming to the. cone figuration ofthegrooved surfaces to which it, is'affixed, and having a portion withinthe groove opposing said selective surface to be plated, insulating allsurfaces of said structure other than said selective surface andthose.covered by said insoluble metallic member and opera? tively connectingsaid member and structure to. positive. and negative poles respectivelyof a' current source. While subjecting said structure to a plating bathuntil, amating' of metal of desired thickness is deposited on said,selective surface.

2. A process of electroplating a selective. surface within a groove of ametallic structure comprised of afiixing insulating material to themember and to. those. surfaces of the groove which are not to be plated,adhesivcly af fixing to a portion of the insulating material aninsolcontour of thesurfaces covered and a portion of. the

tape is disposed within the groove in opposed position to the selectivesurface to be plated, and connecting the tape and structure tothepositive and negative poles of a current source while subjecting thestructure. to a plating bath. i

3. The process of claim 2 wherein the insulating, material is deformableand atfixed to the member ad hesion so that it. conforms to the contourof, the; surfaces covered thereby.

4. The process of claim 2 and adhesively affixing to the outer face ofthe tape a strip of insulating material in sucha position that thecurrent from the tape tothe selective surface is confined within thegroove.

5. A process of chromium plating the land surface of the ring groove ofa piston comprised of afiixing an insulating material by adhesion to thesurfaces of the piston other than the land surface, afiixing to aportion of the material by adhesion a deformable lead tape so that itconforms to the surfaces covered and a portion of the tape is disposedwithin the groove in opposed position to the land surface, andconnecting the tape and piston to the positive and negative poles of acurrent source while subjecting the piston to a chromium plating bath.

6. The process of claim 5 and afiixing to the outer face of the tape byadhesion a second strip of insulation which terminates at the corner ofthe groove opposite the land surface whereby the current from the tapeto the selective surface is confined within the groove.

References Cited in the file of this patent UNITED STATES PATENTS1,335,176 Merritt Mar. 30, 1920 1,798,391 Wurth Mar. 31, 1931 1,809,872Solderberg June 6, 1931 1,845,052 Laukel Feb. 16, 1932 2,710,834Vrilalias June 14, 1955 2,859,157 Curtiss Nov. 4, 1958 FOREIGN PATENTS579,941 Great Britain Aug. 21, 1946

1. A PROCESS OF ELECTROPLATING A SELECTIVE SURFACE WITHIN A GROOVE OF AMETALLIC STRUCTURE COMPRISED OF AFFIXING VIA INSULATING ADHESION ANINSOLUBLE DEFORMABLE METALLIC MEMBER TO THE SURFACES OF THE GROOVE WHICHARE NOT TO BE PLATED, SAID MEMBER CONFORMING TO THE CONFIGURATION OF THEGROOVED SURFACES TO WHICH IT IS AFFIXED AND HAVING A PORTION WITHIN THEGROOVE OPPOSING SAID SELECTIVE SURFACE TO BE PLATED, INSULATING ALLSURFACES OF SAID STRUCTURE OTHER THAN SAID SELECTIVE SURFACE AND THOSECOVERED BY SAID INSOLUBLE METALLIC MEMBER AND OPERATIVELY CONNECTINGSAID MEMBER AND STRUCTURE TO POSITIVE AND NEGATIVE POLES RESPECTIVELY OFA CURRENT SOURCE WHILE SUBJECTING SAID STRUCTURE TO A PLATING BATH UNTILA COATING OF METAL OF DESIRED THICKNESS IS DEPOSITED ON SAID SELECTIVESURFACE.